Optical Illusion Made Tiny Dinos Invisible

Image: A recreation shows the dinosaur Psittacosaurus in a setting where it would be more visible to onlookers. Credit: Jakob Vinther, University of Bristol and Bob Nicholls (Paleocreations.com)

A small dinosaur used an optical illusion to become invisible in dense forests, helping to protect it from larger meat-eating dinos and other predators, a new study shows.

Well-preserved remains of the long-lost species, Psittacosaurus aka "Parrot Lizard," reveal that its body countershading created the camouflage. The findings are presented in the journal Current Biology.

"The fossil preserves clear countershading, which has been shown to function by counter-illuminating shadows on a body, thus making an animal appear optically flat to the eye of the beholder," co-author Jakob Vinther of the University of Bristol said in a press release.

Vinther's University of Bristol colleague, Innes Cuthill, added: "By reconstructing a life-size 3D model, we were able to not only see how the patterns of shading changed over the body, but also that it matched the sort of camouflage which would work best in a forested environment."

Humans and other animals to this day analyze patterns of shadow on an object to help identify what it is. We're usually unaware of this phenomenon. It just happens automatically as part of our visual processing.

The origins of the new study go back to Vinther's work as a Yale graduate student, when he first realized that structures previously thought to be artifacts or dead bacteria in fossilized feathers were actually melanosomes. These are small structures that carry melanin pigments found in the feathers and skin of many animals.

A Psittacosaurus specimen is so well preserved that it shows preserved melanin patterns, which can be seen with the naked eye. Figuring out the distribution of countershading proved to be tricky, though, as the extinct animal had been crushed flat and fossilized.

To overcome these challenges, the researchers asked paleoartist Bob Nicholls to produce what they say is the most scientifically accurate, life-size model made of a dinosaur with its real color patterns.

The researchers next compared the dinosaur's color patterns to the predicted countershading. The results suggest that Parrot Lizard lived in a habitat with a relatively dense canopy, such as a forest.

"We were amazed to see how well these color patterns actually worked to camouflage this little dinosaur," Vinther said.

Parrot Lizard, which Cuthill describes as "both weird and cute, with horns on either side of its head and long bristles on its tail," lived 100-123 million years ago in the early Cretaceous period, in China. Other feathered dinosaurs have been found at the now rocky site where Psittacosaurus was discovered. Plant and wood fossils found in the area support the scientists' belief it was once a forest environment.

Dino species closely related to Parrot Lizard were not forest dwellers, however. They lived in a Mongolian savannah and possibly in other types of habitats. Vinther and his team suspect that those little dinosaurs would have sported different camouflage patterns to match their surroundings.